This invention relates to a maleimide copolymer, a maleimide block copolymer, and a method for producing a block copolymer. More particularly, it relates to a novel maleimide copolymer having peroxy bond in a molecule which is utilized as a precursor for a maleimide block copolymer and as a modifier for other resins. This invention also relates to a maleimide block copolymer which may be produced by polymerizing a maleimide compound and a vinyl monomer using a polymeric peroxide as a polymerization initiator and subsequently polymerizing another vinyl monomer and which may be useful as a molding material, as an additive for improving thermal resistance of other resins or as a compatibilizer for polymer blends and a method for producing such maleimide block copolymer.
As a vinyl polymer having peroxy bond in the molecule, there is disclosed polystyrene having peroxy bond in the molecule in "Kogyo Kagaku Zasshi", by Sugimura et al, Vol. 69, p. 718 (1966), while there are disclosed in Japanese Patent Publication No. 14567/1987 polystyrene, polyvinyl acetate, polymethacrylate or polyvinyl chloride, each having peroxy bond in the molecule. However, no mention has been made of the maleimide polymer in the above publications.
On the other hand, there are also known homopolymers of a maleimide compound and copolymers thereof with vinyl monomers as resins having high thermal resistance. It has also been proposed in Japanese Laid-open Patent Application No. 162543/1986 to add a random copolymer of the maleimide compound and methyl (meth)acrylate to a vinyl chloride resin to improve its thermal resistance.
It is also known to polymerize a vinyl monomer in two stages, using a polymeric peroxide as an initiator, to produce a block copolymer. For example, there is disclosed in Japanese Patent Publication No. 52845/1986 a block copolymer comprised of a methyl (meth)acrylate polymer and polystyrene as unit blocks, while there is disclosed in Japanese Laid-open Patent Application No. 202261/1984 a block copolymer having a wider range of vinyl polymers as block units.
Meanwhile, homopolymers of the maleimide compound has a drawback that, while it is excellent in thermal resistance, it is extremely poor in moldability, while being inferior in compatibility with other resins. Hence, a resin excellent not only in thermal resistance but also in moldability has not yet obtained. On the other hand, no mention is made of the maleimide block copolymer in the aforementioned publications concerning the block copolymers.